Transistor, integrated circuit and method of fabricating the same

ABSTRACT

A transistor, an integrated circuit and a method of fabricating the integrated circuit are provided. In various embodiments, the transistor includes a source electrode, at least one semiconductor channel, a gate electrode, a drain electrode, and a drain pad. The source electrode is disposed in a substrate. The semiconductor channel extends substantially perpendicular to the source electrode. The gate electrode surrounds the semiconductor channel. The drain electrode is disposed on top of the semiconductor channel. The drain pad is disposed on the drain electrode, wherein the drain pad comprises multiple conductive layers.

BACKGROUND

As the integration degree of integrated circuits increases, many efforts have been made to integrate more devices such as transistors within a limited substrate area. In order to reduce the substrate area occupied by one transistor, various vertical transistor structures with a vertical semiconductor channel provided on a substrate have been proposed.

A nanowire field-effect transistor (FET) is one of these vertical transistor structures. In the nanowire FET, a signal current flows through a plurality of vertical nanowires disposed between a source electrode and a drain electrode of the nanowire FET, and the plurality of vertical nanowires is the vertical semiconductor channel between the source electrode and the drain electrode. The vertical semiconductor channel is controlled by a voltage on a vertical gate electrode, which surrounds each of the plurality of vertical nanowires. Therefore, the nanowire FETs are also called vertical gate-all-around (VGAA) field-effect transistors. Among various proposed vertical transistor structures, the nanowire FETs has attracted much attention, and has been regarded as a highly potential candidate for increasing the integration degree of integrated circuits in following generations.

Therefore, various integrated circuits with the nanowire FETs have been proposed. However, technological advances in structure design of integrated circuits with the nanowire FETs are required to overcome various difficulties because requirements in providing the integrated circuits with advanced performances are becoming more challenging. As such, improvements in integrated circuits and methods of fabricating thereof continue to be sought.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a schematic view of at least a portion of an integrated circuit according to various embodiments of the present disclosure.

FIG. 2 is a flowchart illustrating a method of fabricating the integrated circuit according to various embodiments of the present disclosure.

FIG. 3 is a schematic view of at least a portion of the substrate in an intermediate stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure.

FIG. 4 is a schematic view of the substrate shown in FIG. 3 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure.

FIG. 5 is a schematic view of the substrate shown in FIG. 4 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure.

FIG. 6 is a schematic view of the substrate shown in FIG. 5 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure.

FIG. 7 is a schematic view of the substrate shown in FIG. 6 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure.

FIG. 8 is a schematic view of the substrate shown in FIG. 7 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure.

FIG. 9 is a schematic view of the substrate shown in FIG. 8 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure.

FIG. 10 is a schematic view of the substrate shown in FIG. 9 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure.

FIG. 11 is a schematic view of the substrate shown in FIG. 10 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure.

FIG. 12 is a schematic view of the substrate shown in FIG. 11 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure.

FIG. 13 is a schematic view of the substrate shown in FIG. 12 in a subsequent stage of the method of fabricating the integrated circuit according to other various embodiments of the present disclosure.

FIG. 14 is a schematic view of the substrate shown in FIG. 3 in a subsequent stage of the method of fabricating the integrated circuit according to other various embodiments of the present disclosure.

FIG. 15 is a schematic view of at least a portion of an integrated circuit according to various embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

The singular forms “a,” “an” and “the” used herein include plural referents unless the context clearly dictates otherwise. Therefore, reference to, for example, a liner layer includes embodiments having two or more such liner layers, unless the context clearly indicates otherwise. Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Therefore, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Further, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. It should be appreciated that the following figures are not drawn to scale; rather, these figures are intended for illustration.

As aforementioned, requirements in integrated circuits with the nanowire FETs are becoming more challenging. For example, resistances of the integrated circuits with the nanowire FETs such as drain side contact resistivity and interconnect sheet resistance are continually required to be improved. In addition, better process flexibility in fabricating the integrated circuits with the nanowire FETs such as control of drain consumption and silicidation during fabricating the nanowire FETs is also crucial to performance of the integrated circuits with the nanowire FETs fabricated. In this regard, a transistor, an integrated circuit and a method of fabricating the integrated circuit are provided according to various embodiments of the present disclosure.

FIG. 1 is a schematic view of at least a portion of an integrated circuit 10 according to various embodiments of the present disclosure. The integrated circuit 10 includes at least one n-type transistor 100, at least one p-type transistor 200, an inter-layer dielectric 300, and a plurality of contact metals 400. The n-type transistor 100 is disposed on a substrate 15. The p-type transistor 200 is disposed on the substrate 15, and the p-type transistor 200 is adjacent to the n-type transistor 100. The n-type transistor 100 and the p-type transistor 200 are vertical metal-oxide-semiconductor field-effect transistors (MOSFET) such as nanowire FETs formed on the substrate 15, and a shallow trench isolation (STI) 116 is disposed between the n-type transistor 100 and the p-type transistor 200 for isolation. The n-type transistor 100 and the p-type transistor 200 respectively includes a source electrode, at least one semiconductor channel, a gate electrode, a drain electrode, and a drain pad. As illustrated in FIG. 1, the n-type transistor 100 includes a source electrode 110, at least one semiconductor channel 120, a gate electrode 130, a drain electrode 140, and a drain pad 150. The source electrode 110 is disposed in the substrate 15. For example, as shown in FIG. 1, the source electrode 110 could include a doped region 112 formed in the substrate 15, and silicides 114 formed on the doped region 112 as ohmic contacts to the doped region 112. Silicides 114 as the ohmic contacts are often formed by depositing transition metals on the doped region 112 formed in the substrate 15, and forming the silicides by annealing. Silicides 114 as the ohmic contacts could also be deposited by direct sputtering of the compound or by ion implantation of the transition metal followed by annealing.

The semiconductor channel 120 extends substantially perpendicular to the source electrode 110. For example, the semiconductor channel 120 could include an epitaxy 122, a semiconductor pillar 124, and an isolation layer 126 as shown in Figure 1. The epitaxy 122 is formed on the doped region 112. The semiconductor pillar 124 is formed on the epitaxy 122, and surrounded by the isolation layer 126. The gate electrode 130 surrounds the semiconductor channel 120. For example, the gate electrode 130 could include a first metal gate 132, a second metal gate 134, and a gate dielectric layer 136 as shown in FIG. 1. The semiconductor channel 120 is surrounded by the gate dielectric layer 136. The gate dielectric layer 136 is surrounded by the second metal gate 134. Examples of suitable materials for use in the gate dielectric layer 136 include but are not limited to thermally grown silicon dioxide (SiO₂), deposited SiO₂, or a high-k dielectric such as hafnium oxide (HfO₂) deposited by sputter deposition or atomic layer deposition. As used herein, the term “high-k dielectric” refers to dielectrics having a dielectric constant, k, greater than about 4.0, which is higher than the k value of SiO₂. The gate dielectric layer 290 could also include a high-k dielectric material. The high-k material can be defined as a dielectric material having its dielectric constant greater than about 3.9, that of a thermal silicon oxide. For example, the high-k dielectric material could include hafnium oxide (HfO₂), which has a dielectric constant that is in a range from approximately 18 to approximately 40. Alternatively, the high-k material could include one of ZrO₂, Y₂O₃, La₂O₅, Gd₂O₅, TiO₂, Ta₂O₅, HfErO, HfLaO, HfY0, HfGdO, HfAlO, HfZrO, HfTiO, HfTaO, SrTiO, or combinations thereof. The second metal gate 134 is surrounded by the first metal gate 132. The drain electrode 140 is disposed on top of the semiconductor channel 120. For example, the drain electrode 140 could be an epitaxy formed on top of the semiconductor channel 120.

The drain pad 150 is disposed on the drain electrode 140. As illustrated in FIG. 1, the drain pad 150 collects the drain electrodes 140 corresponding to the semiconductor channels 120, and the drain pad 150 could be electrically connected by one of the contact metal 400. It should be noticed that the drain pad 150 includes multiple conductive layers as illustrated in FIG. 1. In other words, the drain pad 150 is not a simple substance, for example, a single titanium silicide (TiSi) film, but the multiple conductive layers as illustrated in FIG. 1. Therefore, drain side contact resistivity and interconnect sheet resistance corresponding to the n-type transistor 100 could be significantly reduced by selecting proper materials and suitable thicknesses of the materials in the multiple conductive layers. As illustrated in FIG. 1, in various embodiments of the present disclosure, the drain pad 150 includes a silicide layer 152, a capping layer 156, and a contact metal layer 158. The silicide layer 152 is in direct contact with the drain electrode 140. The capping layer 156 is disposed on the silicide layer 152. The contact metal layer 158 is disposed on the capping layer 156. As aforementioned, the silicide layer 152 could be formed by depositing transition metals, and annealing the transition metals deposited. In addition, the silicide layer 152 could also be deposited by direct sputtering of the compound or by direct sputtering of the transition metal followed by annealing. In various embodiments of the present disclosure, the silicide layer 152 includes titanium silicide (TiSi), nickel silicide (NiSi), cobalt silicide (CoSi), or combinations thereof. The capping layer 156 disposed on the silicide layer 152 could protects the silicide layer 152 and also could be regarded as a glue layer to combine the silicide layer 152 and the contact metal layer 158. The capping layer 156 could be any suitable conductive material. In various embodiments of the present disclosure, the capping layer 156 includes titanium nitride (TiN), tantalum nitride (TaN), or combinations thereof. The contact metal layer 158 is a metal layer, and therefore has lower resistance than that of the silicide layer 152. In various embodiments of the present disclosure, the contact metal layer 158 includes tungsten (W), aluminum (Al), cobalt (Co), or combinations thereof. As aforementioned, the drain pad 150 is not a simple substance such as a single titanium silicide (TiSi) film, but the multiple conductive layers as illustrated in FIG. 1. Therefore, drain side contact resistivity and interconnect sheet resistance corresponding to the n-type transistor 100 could be significantly reduced by introducing the contact metal layer 158 which has lower resistance than that of the silicide layer 152. Besides, in various embodiments of the present disclosure, the drain pad 150 further includes a metal layer 154 disposed between the silicide layer 152 and the capping layer 156. The metal layer 154 could be any suitable metal material. In various embodiments of the present disclosure, the metal layer 154 includes titanium (Ti), nickel (Ni), cobalt (Co), or combinations thereof. As illustrated in FIG. 1, in various embodiments of the present disclosure, the n-type transistor 100 further includes a passivation layer 160. The passivation layer 160 encapsulates the drain pad 150. In various embodiments of the present disclosure, the passivation layer 160 includes silicon nitride. Therefore, the drain pad 150 could be protected during following fabricating processes, and reliability of the n-type transistor 100 could be further improved.

Also as illustrated in FIG. 1, the p-type transistor 200 includes a source electrode 210, at least one semiconductor channel 220, a gate electrode 230, a drain electrode 240, and a drain pad 250. The source electrode 210 is also disposed in the substrate 15. As shown in FIG. 1, the source electrode 210 could include a doped region 212 formed in the substrate 15, and silicides 214 formed on the doped region 212 as ohmic contacts to the doped region 112. Silicides 214 as the ohmic contacts are often formed by depositing transition metals on the doped region 212 formed in the substrate 15, and forming the silicides by annealing. Silicides 214 could also be deposited by direct sputtering of the compound or by ion implantation of the transition metal followed by annealing. The semiconductor channel 220 extends substantially perpendicular to the source electrode 210. For example, the semiconductor channel 220 could include an epitaxy 222, a semiconductor pillar 224, and an isolation layer 226 as shown in FIG. 1. The epitaxy 222 is formed on the doped region 212. The semiconductor pillar 224 is formed on the epitaxy 222, and surrounded by the isolation layer 226. The gate electrode 230 surrounds the semiconductor channel 220. For example, the gate electrode 230 could include a metal gate 232, and a gate dielectric layer 236 as shown in FIG. 1. The semiconductor channel 220 is surrounded by the gate dielectric layer 236. The gate dielectric layer 236 is surrounded by the metal gate 232. The drain electrode 240 is disposed on top of the semiconductor channel 220. For example, the drain electrode 240 could be an epitaxy formed on top of the semiconductor channel 220. The drain pad 250 is disposed on the drain electrode 240. As illustrated in FIG. 1, the drain pad 250 contacts with the drain electrodes 240 corresponding to the semiconductor channels 220, and the drain pad 250 could be electrically connected by one of the contact metal 400. The drain pad 250 includes multiple conductive layers as illustrated in FIG. 1. In other words, the drain pad 250 is not a simple substance, for example, a single titanium silicide (TiSi) film, but the multiple conductive layers as illustrated in FIG. 1. Therefore, drain side contact resistivity and interconnect sheet resistance corresponding to the p-type transistor 200 could be significantly reduced by selecting proper materials and suitable thicknesses of the materials in the multiple conductive layers. As illustrated in FIG. 1, in various embodiments of the present disclosure, the drain pad 250 includes a silicide layer 252, a capping layer 256, and a contact metal layer 258. The silicide layer 252 is in direct contact with the drain electrode 240. The capping layer 256 is disposed on the silicide layer 252. The contact metal layer 258 is disposed on the capping layer 256. As aforementioned, the silicide layer 252 could be formed by depositing transition metals, and annealing the transition metals deposited. In addition, the silicide layer 252 could also be deposited by direct sputtering of the compound or by direct sputtering of the transition metal followed by annealing. In various embodiments of the present disclosure, the silicide layer 252 includes titanium silicide (TiSi), nickel silicide (NiSi), cobalt silicide (CoSi), or combinations thereof. The capping layer 256 disposed on the silicide layer 252 could protects the silicide layer 252 and also could be regarded as a glue layer to combine the silicide layer 252 and the contact metal layer 256. The capping layer 256 could be any suitable conductive material. In various embodiments of the present disclosure, the capping layer 156 includes titanium nitride (TiN), tantalum nitride (TaN), or combinations thereof. The contact metal layer 258 is a metal layer, and therefore has lower resistance than that of the silicide layer 252. In various embodiments of the present disclosure, the contact metal layer 258 includes tungsten (W), aluminum (Al), cobalt (Co), or combinations thereof. As aforementioned, the drain pad 250 is not a simple substance such as a single titanium silicide (TiSi) film, but the multiple conductive layers as illustrated in FIG. 1. Therefore, drain side contact resistivity and interconnect sheet resistance corresponding to the p-type transistor 200 could be significantly reduced by introducing the contact metal layer 258 which has lower resistance than that of the silicide layer 252. Besides, in various embodiments of the present disclosure, the drain pad 250 further includes a metal layer 254 disposed between the silicide layer 252 and the capping layer 256. The metal layer 254 could be any suitable metal material. In various embodiments of the present disclosure, the metal layer 254 includes titanium (Ti), nickel (Ni), cobalt (Co), or combinations thereof. As illustrated in FIG. 1, in various embodiments of the present disclosure, the p-type transistor 200 further includes a passivation layer 260. The passivation layer 260 encapsulates the drain pad 250. In various embodiments of the present disclosure, the passivation layer 260 includes silicon nitride. Therefore, the drain pad 250 could be protected during following fabricating processes, and reliability of the p-type transistor 200 could be further improved.

As illustrated in FIG. 1, the inter-layer dielectric 300 covers the n-type transistor 100, the p-type transistor 200, and the substrate 15. The inter-layer dielectric 300 could be formed by depositing silicon oxide in any suitable depositing processes, including but not limited to, atomic layer deposition (ALD), chemical vapor deposition (CVD), low-pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD), high density plasma chemical vapor deposition (HDPCVD), sub-atmospheric chemical vapor deposition (SACVD), rapid thermal chemical vapor deposition (RTCVD), high temperature oxide deposition (HTO), low temperature oxide deposition (LTO), limited reaction processing CVD (LRPCVD). The plurality of contact metals 400 is disposed in the inter-layer dielectric 300, and the contact metals 400 are respectively in direct contact with the source electrodes 110, 210, the gate electrodes 130, 230, and the drains pad 150, 250 of the n-type transistor 100 and the p-type transistor 200.

FIG. 2 is a flowchart illustrating a method 800 of fabricating the integrated circuit according to various embodiments of the present disclosure. The method 800 begins with block 802 in which a substrate is received. The substrate could be a semiconductor substrate including single crystalline silicon that has been slightly doped with n-type or p-type dopants. The substrate has at least one n-type transistor and at least one p-type transistor. The n-type transistor and the p-type transistor respectively includes a source electrode disposed in the substrate, at least one semiconductor channel extending substantially perpendicular to the source electrode, a gate electrode surrounding the semiconductor channel, and a drain electrode disposed on top of the semiconductor channel. The method 800 continues with block 804 in which a capping layer and a silicide layer is formed. The silicide layer covers the drain electrodes of the n-type transistor and the p-type transistor. The capping layer is formed on the silicide layer. The method 800 continues with block 806 in which a metal layer is formed. The metal layer covers the capping layer. The method 800 continues with block 808 in which a first passivation layer is formed. The first passivation layer covers the metal layer. The method 800 further includes forming a opening through the silicide layer, the capping layer, the metal layer, and the first passivation layer to yield respective drain pads disposed on the drain electrodes of the n-type transistor and the p-type transistor as shown in block 810. The method 800 further includes forming a second passivation layer covering sidewalls of the drain pads as shown in block 812. The method 800 further includes forming an first oxide layer to fulfill gaps between the sidewalls of the drain pads and cover the first passivation layer as shown in block 814. The method 800 continues with block 816 in which the first oxide layer is polished. The polishing stops at the first passivation layer. The method 800 continues with block 818 in which an inter-layer dielectric is formed. The inter-layer dielectric covers the n-type transistor, the p-type transistor, and the substrate. The method 800 further includes forming a plurality of contact metals disposed in the inter-layer dielectric, and the contact metals being respectively in direct contact with the source electrodes, the gate electrodes, and the drains pad of the n-type transistor and the p-type transistor as shown in block 820. The details of the methods 800 are further illustrated in FIGS. 3-13 and described in following paragraphs.

FIG. 3 is a schematic view of at least a portion of the substrate in an intermediate stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure. Referring to FIG. 3, a substrate 15 is received. The substrate 15 has at least one n-type transistor 100 and at least one p-type transistor 200. The n-type transistor 100 and the p-type transistor 200 respectively comprises a source electrode disposed in the substrate, at least one semiconductor channel extending substantially perpendicular to the source electrode, a gate electrode surrounding the semiconductor channel, and a drain electrode disposed on top of the semiconductor channel. As shown in FIG. 3, the n-type transistor 100 includes a source electrode 110, at least one semiconductor channel 120, a gate electrode 130, and a drain electrode 140. The details of the source electrode 110, the semiconductor channel 120, the gate electrode 130, and the drain electrode 140 of the n-type transistor 100 are similar to those aforementioned, and therefore the details are omitted here. The p-type transistor 200 includes a source electrode 210, at least one semiconductor channel 220, a gate electrode 230, and a drain electrode 240. The details of the source electrode 210, the semiconductor channel 220, the gate electrode 230, and the drain electrode 240 of the p-type transistor 200 are also similar to those aforementioned, and therefore the details are omitted here. As illustrated in FIG. 3, a passivation film 610 such as silicon nitride and a dielectric film 310 such as silicon oxide could be conformally deposited to cover the n-type transistor 100 and the p-type transistor 200, and the passivation film 610 and the dielectric film 310 could be planarized by polishing and/or etched to expose respective drain electrodes 140, 240 of the n-type transistor 100 and the p-type transistor 200.

FIG. 4 is a schematic view of the substrate shown in FIG. 3 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure. FIG. 5 is a schematic view of the substrate shown in FIG. 4 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure. Referring to FIG. 4 and FIG. 5, after the operation of receiving the substrate 15 having at least one n-type transistor 100 and at least one p-type transistor 200, a silicide layer 540 is formed. The silicide layer 540 covers the drain electrodes 140, 240 of the n-type transistor 100 and the p-type transistor 200. The silicide layer 540 could be formed in directly depositing a silicide film such as titanium silicide (TiSi), nickel silicide (NiSi), cobalt silicide (CoSi) to cover the drain electrode 140 of the n-type transistor 100 and the drain electrode 240 of the p-type transistor 200. The silicide layer 540 could be formed by multiple steps. As illustrated in FIG. 4, in various embodiments of the present disclosure, the operation forming the silicide layer 540 covering the drain electrodes 140, 240 of the n-type transistor 100 and the p-type transistor 200 includes depositing an amorphous silicon layer 510 covering the drain electrodes 140, 240 of the n-type transistor 100 and the p-type transistor 200. Next, a first metal layer 520 is deposited to cover the amorphous silicon layer 510. The first metal layer 520 could include titanium (Ti), nickel (Ni), cobalt (Co), or combinations thereof. The amorphous silicon layer 510 and the first metal layer 520 are annealed to convert the amorphous silicon layer 510 to the silicide layer 540 as shown in FIG. 5. The annealing process such as rapid thermal annealing (RTA) could be performed for converting the amorphous silicon layer 510. In various embodiments of the present disclosure, the first metal layer 520 is also converted to the silicide layer 540. Also as illustrated in FIG. 5, after the silicide layer 540 is formed, a capping layer 530 is formed. The capping layer 530 covers the silicide layer 540. The capping layer 530 could include titanium nitride (TiN). In some embodiments, the capping layer 530 is formed on the first metal layer 520 before annealing the amorphous silicon layer 510.

FIG. 6 is a schematic view of the substrate shown in FIG. 5 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure. FIG. 7 is a schematic view of the substrate shown in FIG. 6 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure. Referring to FIG. 6, after the operation of forming the capping layer 530 covering the silicide layer 540, a metal layer 550 is formed to cover the capping layer 530. The metal layer 550 could include tungsten (W). As illustrated in FIG. 6, after the operation of forming the metal layer 550 covering the capping layer 530, a first passivation layer 610 is formed. The first passivation layer 610 covers the metal layer 550. The first passivation layer 610 could include silicon nitride, and be formed in any suitable depositing processes, including but not limited to, atomic layer deposition (ALD), chemical vapor deposition (CVD), low-pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD), high density plasma chemical vapor deposition (HDPCVD), sub-atmospheric chemical vapor deposition (SACVD), rapid thermal chemical vapor deposition (RTCVD), high temperature oxide deposition (HTO), low temperature oxide deposition (LTO), limited reaction processing CVD (LRPCVD). Referring to FIG. 7, after the operation of forming the first passivation layer 610 covering the metal layer 550, a opening 650 through the silicide layer 540, the capping layer 530, the metal layer 550, and the first passivation layer 610 is formed to yield respective drain pads 150, 250 disposed on the drain electrodes 140, 240 of the n-type transistor 100 and the p-type transistor 200. In other words, the silicide layer 540, the capping layer 530, and the metal layer 550 formed in pervious operations are separated into drain pads 150, 250 respectively disposed on the drain electrodes 140, 240 of the n-type transistor 100 and the p-type transistor 200. The drain pads 150 of the n-type transistor 100 includes a silicide layer 152, a capping layer 156, and a contact metal layer 158, and the drain pad 250 of the p-type transistor 200 includes a silicide layer 252, a capping layer 256, and a contact metal layer 258. In various embodiments of the present disclosure, the drain pads 150 of the n-type transistor 100 further include a metal layer 154, and the drain pads 250 of the p-type transistor 200 further include a metal layer 254 as shown in FIG. 7.

FIG. 8 is a schematic view of the substrate shown in FIG. 7 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure. FIG. 9 is a schematic view of the substrate shown in FIG. 8 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure. Referring to FIG. 8, after the operation of forming the opening 650 through the silicide layer 540, the capping layer 530, the metal layer 550, and the first passivation layer 610, a second passivation layer 620 is formed covering sidewalls of the drain pads 150, 250. The second passivation layer 620 could include silicon nitride as the first passivation layer 610, and be formed in any suitable depositing processes, including but not limited to, atomic layer deposition (ALD), chemical vapor deposition (CVD), low-pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD), high density plasma chemical vapor deposition (HDPCVD), sub-atmospheric chemical vapor deposition (SACVD), rapid thermal chemical vapor deposition (RTCVD), high temperature oxide deposition (HTO), low temperature oxide deposition (LTO), limited reaction processing CVD (LRPCVD). Therefore, the drain pad 150 of the n-type transistor 100 and the drain pad 250 of the p-type transistor 200 could be further protected, and the reliability of the n-type transistor 100 and the p-type transistor 200 could be further improved. Referring to FIG. 9, the second passivation layer 620 could be further etched to be planarized and part of the second passivation layer 620 is removed for following processes.

FIG. 10 is a schematic view of the substrate shown in FIG. 9 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure. FIG. 11 is a schematic view of the substrate shown in FIG. 10 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure. Referring to FIG. 10, after the operation of forming the second passivation layer 620 covering sidewalls of the drain pads 150, 250, an first oxide layer 630 is formed to fulfill gaps between the sidewalls of the drain pads 150, 250. The first oxide layer 630 could include silicon oxide and be formed in any suitable depositing processes. In various embodiments of the present disclosure, the forming the first oxide layer 630 to fulfill gaps between the sidewalls of the drain pads 150, 250 is performed by flowable CVD. Therefore, gaps between the sidewalls of the drain pads 150, 250 could be fulfilled without voids, and the reliability of the n-type transistor 100 and the p-type transistor 200 could be further improved. Referring to FIG. 11, after the operation of forming the first oxide layer 630, the first oxide layer 630 is polished. It should be noticed that the polishing stops at the first passivation layer 610 because the first passivation layer 610 includes silicon nitride which is different from the first oxide layer 630. Therefore, process window of the polishing is increased, and the uniformity of thickness of the drain pads 150, 250 could be improved.

FIG. 12 is a schematic view of the substrate shown in FIG. 11 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure. FIG. 13 is a schematic view of the substrate shown in FIG. 12 in a subsequent stage of the method of fabricating the integrated circuit according to other various embodiments of the present disclosure. Referring to FIG. 12, after the operation of polishing the first oxide layer 630, an inter-layer dielectric 640 is formed. The inter-layer dielectric 640 covers the n-type transistor 100, the p-type transistor 200, and the substrate 15. The inter-layer dielectric (ILD) layer 640 could include any now known or later developed dielectric appropriate for a first contact layer such as but not limited to: silicon nitride (Si₃N₄), silicon oxide (SiO₂), fluorinated SiO₂ (FSG), hydrogenated silicon oxycarbide (SiCOH), porous SiCOH, boro-phosho-silicate glass (BPSG), silsesquioxanes, carbon (C) doped oxides (i.e., organosilicates) that include atoms of silicon (Si), carbon (C), oxygen (0), and/or hydrogen (H), thermosetting polyarylene ethers, a spin-on silicon-carbon containing polymer materials, other low dielectric constant material, or layers thereof. In various embodiments of the present disclosure, the ILD layer 230 could include high dielectric (high-k) dielectrics such as metal oxides such as tantalum oxide (Ta₂O₅), barium titanium oxide (BaTiO₃), hafnium oxide (HfO₂), zirconium oxide (ZrO₂), aluminum oxide (Al₂O₃). After the operation of forming the inter-layer dielectric 640, a plurality of contact metals 400 is formed. Referring to FIG. 13, a plurality of openings could be formed by litho-etching processes to expose the source electrodes 110, 210, the gate electrodes 130, 230, and the drains pad 150, 250 of the n-type transistor 100 and the p-type transistor 200. Then a contact metal film 410 could be formed on the inter-layer dielectric 300 (including the first oxide layer 630 and the an inter-layer dielectric 640) as illustrated in FIG. 13. As illustrated in FIG. 13, the contact metal film 410 is disposed in the inter-layer dielectric 300, and the contact metals 400 are respectively in direct contact with the source electrodes 110, 210, the gate electrodes 130, 230, and the drains pad 150, 250 of the n-type transistor 100 and the p-type transistor 200. The contact metal film 410 is polished to yield the plurality of contact metals 400 as illustrated in FIG. 1. Therefore, the integrated circuit 10 illustrated in FIG. 1 according to various embodiments of the present disclosure is fabricated. The plurality of contact metals 400 could also include tungsten, aluminum, copper, or other suitable materials.

FIG. 14 shows forming a capping layer and a silicide layer covering the drain electrodes of the n-type transistor and the p-type transistor as shown in block 804 of the method 800 according to various embodiments. FIG. 14 is a schematic view of the substrate shown in FIG. 3 in a subsequent stage of the method of fabricating the integrated circuit according to various embodiments of the present disclosure. Referring to FIG. 14, after the operation of receiving the substrate 15 having at least one n-type transistor 100 and at least one p-type transistor 200, a silicide layer 710 and a capping layer 730 are formed. The silicide layer 710 covers the drain electrodes 140, 240 of the n-type transistor 100 and the p-type transistor 200. The silicide layer 710 could include titanium silicide (TiSi), nickel silicide (NiSi), cobalt silicide (CoSi), or combinations thereof to cover the drain electrode 140 of the n-type transistor 100 and the drain electrode 240 of the p-type transistor 200. The silicide layer 710 could be formed by multiple steps. As illustrated in FIG. 14, in various embodiments of the present disclosure, the operation forming the capping layer 730 and the silicide layer 710 covering the drain electrodes 140, 240 of the n-type transistor 100 and the p-type transistor 200 includes depositing a first metal layer 720 covering the drain electrodes 140, 240 of the n-type transistor 100 and the p-type transistor 200. The first metal layer 720 could include titanium (Ti), nickel (Ni), cobalt (Co), or combinations thereof. Next, the drain electrodes 140, 240 of the n-type transistor 100 and the p-type transistor 200 and the first metal layer 720 are annealed to convert part of the drain electrodes 140, 240 to the silicide layer 710 as shown in FIG. 14. The volume of the drain electrodes 140, 240 are thus decreased, after the silicide layers 710 are formed. The annealing process such as rapid thermal annealing (RTA) could be performed for forming the silicide layer 710. Then the capping layer 730 is formed on the first metal layer 720. The capping layer 730 covers the first metal layer 720. The capping layer 730 could include titanium nitride (TiN), tantalum nitride (TaN), or combinations thereof. In some embodiments, the capping layer 730 may be formed before the annealing process. For example, the operation forming the capping layer 730 and the silicide layer 710 covering the drain electrodes 140, 240 of the n-type transistor 100 and the p-type transistor 200 may include depositing a first metal layer 720 covering the drain electrodes 140, 240 of the n-type transistor 100 and the p-type transistor 200. Next, a capping layer 730 is formed on the first metal layer 720. Then the drain electrodes 140, 240 of the n-type transistor 100 and the p-type transistor 200 and the first metal layer 720 are annealed to convert part of the drain electrodes 140, 240 to the silicide layer 710 as shown in FIG. 14.

FIG. 15 is a schematic view of at least a portion of an integrated circuit according to various embodiments of the present disclosure. Referring to FIGS. 1, 2 and 15, the substrate shown in FIG. 15 is the substrate shown in FIG. 14 after operating the method 800 from block 808 to block 822. The differences between the integrated circuit 10 in FIG. 15 and FIG. 1 include a drain electrode 141 of the n-type transistor 100, a drain pad 151 of the n-type transistor 100, a drain electrode 241 of the p-type transistor 200, and a drain pad 251 the p-type transistor 200. The drain pad 151 of the n-type transistor 100 includes a silicide layer 153, a metal layer 155, a capping layer 157, and a contact metal layer 159. The silicide layer 153 is in direct contact with the drain electrode 141. The metal layer 155 is disposed on the silicide layer 153. The capping layer 157 is disposed on the silicide layer 153. The contact metal layer 159 is disposed on the capping layer 157. The drain pad 251 of the p-type transistor 200 includes a silicide layer 253, a metal layer 255, a capping layer 257, and a contact metal layer 259. The silicide layer 253 is in direct contact with the drain electrode 241. The metal layer 255 is disposed on the silicide layer 253. The capping layer 257 is disposed on the silicide layer 253. The contact metal layer 259 is disposed on the capping layer 257. In various embodiments of the present disclosure, the silicide layers 153, 253 include titanium silicide (TiSi), nickel silicide (NiSi), cobalt silicide (CoSi), or combinations thereof. In various embodiments of the present disclosure, the metal layers 155, 255 include titanium (Ti), nickel (Ni), cobalt (Co), or combinations thereof. In various embodiments of the present disclosure, the capping layers 157, 257 include titanium nitride (TiN), tantalum nitride (TaN), or combinations thereof. In various embodiments of the present disclosure, the contact metal layers 159, 259 include tungsten (W), aluminum (Al), cobalt (Co), or combinations thereof.

According to other various embodiments of the present disclosure, resistances of the integrated circuits with the transistors such as drain side contact resistivity and interconnect sheet resistance are significantly reduced because of special design of the drain pad with multiple conductive layers. As aforementioned, the drain pad of the transistors is not a simple substance such as a single silicide film, but the multiple conductive layers. Therefore, drain side contact resistivity and interconnect sheet resistance correlated to the transistors could be significantly reduced by introducing the contact metal layer which has lower resistance than that of the silicide layer. In addition, process flexibility in fabricating the integrated circuits with the transistors such as control of drain consumption and silicidation during fabricating the transistors is also improved, and therefore performance of the integrated circuits with the transistors according to various embodiments of the present disclosure is enhanced.

According to other various embodiments of the present disclosure, the transistor includes a source electrode, at least one semiconductor channel, a gate electrode, a drain electrode, and a drain pad. The source electrode is disposed in a substrate. The semiconductor channel extends substantially perpendicular to the source electrode. The gate electrode surrounds the semiconductor channel. The drain electrode is disposed on top of the semiconductor channel. The drain pad is disposed on the drain electrode, wherein the drain pad comprises multiple conductive layers.

According to other various embodiments of the present disclosure, the integrated circuit includes at least one n-type transistor, at least one p-type transistor, an inter-layer dielectric, and a plurality of contact metals. The n-type transistor is disposed on a substrate. The p-type transistor is disposed on the substrate and is adjacent to the n-type transistor. The n-type transistor and the p-type transistor respectively includes a source electrode disposed in the substrate, at least one semiconductor channel extending substantially perpendicular to the source electrode, a gate electrode surrounding the semiconductor channel, a drain electrode disposed on top of the semiconductor channel, and a drain pad disposed on the drain electrode. The drain pad includes multiple conductive layers. The inter-layer dielectric covers the n-type transistor, the p-type transistor, and the substrate. The plurality of contact metals is disposed in the inter-layer dielectric, and the contact metals are respectively in direct contact with the source electrodes, the gate electrodes, and the drains pad of the n-type transistor and the p-type transistor.

According to various embodiments of the present disclosure, a method of fabricating the integrated circuit includes receiving a substrate having at least one n-type transistor and at least one p-type transistor, wherein each of the n-type transistor and the p-type transistor comprises a source electrode disposed in the substrate, at least one semiconductor channel extending substantially perpendicular to the source electrode, a gate electrode surrounding the semiconductor channel, and a drain electrode disposed on top of the semiconductor channel. The method further includes forming a capping layer and a silicide layer covering the drain electrodes of the n-type transistor and the p-type transistor, wherein the capping layer is formed on the silicide layer. The method further includes forming a metal layer covering the capping layer. The method further includes forming a first passivation layer covering the metal layer. The method further includes forming a opening through the silicide layer, the capping layer, the metal layer, and the first passivation layer to yield respective drain pads disposed on the drain electrodes of the n-type transistor and the p-type transistor. The method further includes forming a second passivation layer covering sidewalls of the drain pads. The method further includes forming a first oxide layer to fulfill gaps between the sidewalls of the drain pads and cover the first passivation layer. The method further includes polishing the first oxide layer, wherein the polishing stops at the first passivation layer. The method further includes forming an inter-layer dielectric covering the n-type transistor, the p-type transistor, and the substrate. The method further includes forming a plurality of contact metals disposed in the inter-layer dielectric, and the contact metals being respectively in direct contact with the source electrodes, the gate electrodes, and the drains pad of the n-type transistor and the p-type transistor.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A transistor, comprising: a source electrode disposed in a substrate; at least one semiconductor channel extending substantially perpendicular to the source electrode; a gate electrode surrounding the semiconductor channel; a drain electrode disposed on a top of the semiconductor channel; a drain pad disposed on the drain electrode, wherein the drain pad comprises a silicide layer having a recess on the drain electrode, a conductive capping layer disposed on the silicide layer, and a contact metal layer disposed on the conductive capping layer, the drain electrode has a top portion embedded in the recess of the silicide layer, and the silicide layer has a greater thickness than the conductive capping layer; and a passivation layer encapsulating the drain pad.
 2. The transistor of claim 1, wherein the silicide layer comprises titanium silicide, nickel silicide, cobalt silicide, or combinations thereof.
 3. The transistor of claim 1, wherein the conductive capping layer comprises titanium nitride (TiN), tantalum nitride (TaN), or combinations thereof.
 4. The transistor of claim 1, wherein the contact metal layer comprises tungsten, aluminum, cobalt, or combinations thereof.
 5. The transistor of claim 1, wherein the drain pad further comprises a metal layer disposed between the silicide layer and the conductive capping layer.
 6. The transistor of claim 5, wherein the metal layer comprises titanium (Ti), nickel (Ni), cobalt (Co), or combinations thereof.
 7. An integrated circuit, comprising: at least one n-type transistor disposed on a substrate; at least one p-type transistor disposed on the substrate and adjacent to the n-type transistor, wherein each one of the n-type transistor and the p-type transistor comprises: a source electrode disposed in the substrate; at least one semiconductor channel extending substantially perpendicular to the source electrode; a gate electrode surrounding the semiconductor channel; a drain electrode disposed on a top of the semiconductor channel; a drain pad disposed on the drain electrode, wherein the drain pad comprises a silicide layer having a recess on the drain electrode, a conductive capping layer disposed on the silicide layer, and a contact metal layer disposed on the conductive capping layer, the drain electrode has a top portion embedded in the recess of the silicide layer, and the silicide layer has a first portion on a sidewall of the drain electrode and a second portion that extends from the first portion away from the drain electrode; and a passivation layer encapsulating the drain pad; an inter-layer dielectric covering the n-type transistor, the p-type transistor, and the substrate; and a plurality of contact metals disposed in the inter-layer dielectric, and the contact metals being respectively in direct contact with the source electrodes, the gate electrodes, and the drain pads of the n-type transistor and the p-type transistor.
 8. The integrated circuit of claim 7, wherein the silicide layer comprises titanium silicide, nickel silicide, cobalt silicide, or combinations thereof.
 9. The integrated circuit of claim 7, wherein the conductive capping layer comprises titanium nitride (TiN), tantalum nitride (TaN), or combinations thereof.
 10. The integrated circuit of claim 7, wherein the contact metal layer comprises tungsten, aluminum, cobalt, or combinations thereof.
 11. The integrated circuit of claim 7, further comprising a metal layer disposed between the silicide layer and the conductive capping layer.
 12. The integrated circuit of claim 7, wherein the metal layer comprises titanium (Ti), nickel (Ni), cobalt (Co), or combinations thereof.
 13. The transistor of claim 1, wherein the passivation layer comprises silicon nitride.
 14. The integrated circuit of claim 7, wherein the contact metal layer has a resistance lower than a resistance of the silicide layer.
 15. The integrated circuit of claim 7, wherein the passivation layer comprises silicon nitride.
 16. The transistor of claim 1, wherein the passivation layer covers a sidewall of the contact metal layer.
 17. The transistor of claim 1, wherein the passivation layer covers over a top surface of the contact metal layer.
 18. The integrated circuit of claim 7, wherein the passivation layer covers a sidewall of the contact metal layer.
 19. The integrated circuit of claim 7, wherein the passivation layer covers over a top surface of the contact metal layer.
 20. A transistor, comprising: a source electrode disposed in a substrate; at least one semiconductor channel extending substantially perpendicular to the source electrode; a gate electrode surrounding the semiconductor channel; a drain electrode disposed on a top of the semiconductor channel; a drain pad disposed on the drain electrode, wherein the drain pad comprises a silicide layer having a recess on the drain electrode, a conductive capping layer disposed on the silicide layer, and a contact metal layer disposed on the conductive capping layer, the drain electrode has a top portion embedded in the recess of the silicide layer, the contact metal layer has a resistance lower than a resistance of the silicide layer, and the conductive capping layer has a first portion on a sidewall of the silicide layer and a second portion that extends from the first portion away from the sidewall of the silicide layer; and a passivation layer encapsulating the drain pad. 